cluster-receiver: update SRCREV

Update SRCREV to pick up:

6ac9d95 Bump agl-shell protocol version

Bug-AGL: SPEC-4793

Change-Id: I2e7a486c48dcafd893aae67f7d356076914be68e
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29458
Reviewed-by: Marius Vlad <marius.vlad@collabora.com>
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>